Electrophysiology of extrafetal membranes.

This paper reviews some of the equations that apply to the electrophysiology of the extrafetal membranes, and stresses the limitations that may apply to the use of these equations. A literature review of experimental data on potential differences between the fetus, the extrafetal fluid compartments and the mother leads to the conclusion that the transplacental potential difference is no more than a few millivolts and that, in some species, there is an electrical generator outside the placenta.